Functional characteristics of plitidepsin as an antiviral treatment against monkeypox virus infection

Monkeypox virus (MPXV), closely related to variola virus, causes mpox, a zoonotic disease traditionally endemic to Central Africa. However, recent outbreaks have increased human transmission of MPXV clades. In 2022, global MPXV spread was linked to clade IIb, whereas in 2024, the more pathogenic clade Ib became predominant. These trends raised concerns about sustained human transmission, prompting the WHO to declare mpox a Public Health Emergency of International Concern. Despite the availability of smallpox vaccines, their protective efficacy against mpox remains limited. Additionally, the limited efficacy of current smallpox antivirals, such as Tecovirimat and Brincidofovir, alongside growing concerns about the emergency of tecovirimat resistance mutants, underscores the need for new therapeutic options. Given these challenges, novel antiviral strategies with different mechanisms of action are urgently needed to control MPXV outbreaks. Plitidepsin, a cyclodepsipeptide drug initially approved for cancer treatment, has demonstrated potent antiviral activity against multiple viruses by targeting eukaryotic elongation factor 1 alpha (eEF1A). Here, we have evaluated the antiviral activity of plitidepsin against MPXV infection. In cultured cells, plitidepsin exhibited strong antiviral effects, with a favorable therapeutic index and low cytotoxicity. In CAST/EiJ mice, a highly susceptible MPXV model, plitidepsin significantly reduced viral replication in the lungs. Additionally, treated mice displayed a marked reduction in inflammatory lung lesions and proinflammatory cytokines, suggesting immunomodulatory effects. These findings indicate plitidepsin as a promising candidate for mpox treatment. Further studies are needed to explore its potential as a standalone or combination therapy, supporting clinical evaluation for mpox treatment.